Waveguide side wall slot radiator



July 21, 1970 L. F

WAVEGUIDE SIDE WALL SLOT RADIATOR 5 Sheets-Sheet 1 Filed NOV. 12. 1968 t v WH W; I, z w W July 21, 1970 M. FEE 3,521,287

WAVEGUIDE SIDE WALL SLOT RADIATOR Filed Nov. 12. 1968 5 Sheets- Sheet 2 lira-2.

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July 21, 1970 I M, L, FEE 3,521,281

WAVEGUIDE SIDE WALL SLOT RADIATOR Filed Nov. 12, 1968 3 S heets-S heet I5 United States Patent O US. Cl. 343-771 3 Claims ABSTRACT OF THE DISCLOSURE A radiating element in accordance with the present invention constitutes a slot cut transversely in the narrow side wall of a rectangular waveguide with the ends of the slot extending into the broad wall of the waveguide. One end of the slot extends into the broad wall a greater distance than the corresponding opposite end whereby the slot is excited with a sense of excitation determined by the broad wall into which the slot extension has increased. In an array design, the slots are spaced approximately half a guide wavelength apart with adjacent slots extending into opposite broad walls thereby to maintain proper phase relationship. For light coupling, resonant slots may be used; for heavy coupling, non-resonant slots are used to permit the slot to extend further into the broad wall. These slots may :be used in conjunction with longitudinal shunt slots to provide a circularly polarized planar antenna.

BACKGROUND OF THE INVENTION Contemporary waveguide side wall slots, also referred to as edge slots or narrow face slots, appear as shunt elements on an equivalent TE -mode transmission line. These slots are cut into the side wall of rectangular waveguide and are angled with respect to a line perpendicular to the direction of propagation of electromagnetic energy in the waveguide. Side wall currents are perpendicular to the direction of propagation of energy in the waveguide and will not excite a side wall slot unless it is angled. The coupling of the angled side wall slot increases as its angle is increased. The electric field of this slot is polarized with its main component in the direction of propagation in the guide and an undesirable component at right angles to the main component as a result of the slot angle. This latter undesirable component constitutes a loss in aperture efficiency, particularly when heavy coupling (large angles) is used.

One method of eliminating the undesired cross polarized component is to use a side wall slot which is not angled and to excite it by using a hook probe. The disadvantage of this method is that it increases the complexity of the array design, and in addition, makes the array more frequency sensitive. In addition, arrays using angled side wall slots have been built with external bafiles to suppress the cross polarization component. The use of external bafiies has the disadvantage of increasing the weight of an array.

SUMARY OF THE INVENTION In accordance with the present invention, radiating elements are provided by one or more slots cut transversely across the narrow side wall of a rectangular waveguide with the ends of the slot extending different distances into the broad wall of the waveguide. For the case when each end of the slot extends the same distance in each broad wall, longitudinal currents of equal magnitude and opposite sense are interrupted which results in no excitation of the slot. Decreasing the extension of the slot in one broad wall and increasing it in the other results in the slot being excited with the sense of excitation being determined by the broad wall into which the slot extension was increased.

3,521,287 Patented July 21, 1970 In a typical array the slots are spaced approximately half a guide wavelength apart with adjacent slots extending into opposite broad walls to maintain the proper phase relationship. A circularly polarized antenna is provided by interspacing linear arrays of longitudinal shunt slots between linear arrays of transverse slots in accordance with the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a waveguide linear array of 10 radiating slots with side reflectors;

FIG. 2 shows the E-plane power distribution pattern of the linear array of FIG. 1;

FIG. 3 shows the H-plane power distribution pattern of the linear array of FIG. 1; and

FIG. 4 shows a portion of a circular polarized planar antenna provided by longitudinal shunt slots interspaced between linear arrays of the device of FIG. 1.

Referring to FIG. 1 of the drawings, there is shown a linear array 10 in accordance with the present invention. The linear array 10 comprises a straight section of rectangular waveguide 12 having flanges 13, 14 at opposite extremities thereof. Transverse slots 16, 18, 20, 22, 24 are disposed along the narrow wall of waveguide 12, one guide wavelength apart. In addition, transverse slots 15, 17, 19, 21, 23 are disposed along the narrow wall of waveguide 12 one wavelength apart intermediate the slots 16, 18, 20, 22, 24, thereby forming a linear array of slots 15-24 along the narrow wall of waveguide 12 spaced one-half guide wavelength apart.

The slots 15, 17, 19, 21, 23 extend into the broad walls of waveguide 12 with the near extremities, as viewed in the drawing, extending of the order of /8 the distance across the broad wall of waveguide 12 and the opposite extremities thereof extending of the order of A the distance across the opposite broad wall, as illustrated by the cutaway from slot 17. Slots 16, 18, 20, 22, 24, on the other hand, extend into the broad walls of waveguide 12 with the near extremities, as viewed in the drawing, extending of the order of A the distance across the broad wall of waveguide 12 and the opposite extremities thereof extending of the order of /8 the distance across the opposite broad wall.

Reflectors 26, 28 are disposed normal to the broad walls of waveguide 12 of the order of the distance thereacross from the narrow wall containing the slots 15-24. The reflectors 26, 28 have a width of the order of that of the broad walls of waveguide 12 and extend one-guide wavelength past the slots 15, 24 at the extremities at the linear array of slots 15-24. The reflectors 26, 28 may have an L-shape configuration and may, for example, be dip brazed to the broad wall of waveguide 12.

The linear array 10 of FIG. 1 when appropriately energized, generates a fan-shaped beam of the order of 20 in width. Relative power pattern 30, FIG. 2, illustrates the E-plane characteristic of this fan-shaped beam generated by the linear array 10 and relative power pattern 32, FIG. .3, illustrates the H-plane characteristic thereof.

Referring to FIG. 4, there is shown a portion of a twodimensional circularly polarized planar array composed of linear arrays 10 interspaced with linear arrays 33 of longitudinal slots in the broad walls of waveguides 34 extending between the waveguides 12 of linear array 10. In general, the broad walls of the waveguides 34 replace the reflectors 26, 28 of the linear array 10 of FIG. 1. The longitudinal slots of the linear arrays 33 alternate across the broad wall of waveguides 34 and are spaced one-half guide wavelength apart. The transverse slots of linear array 10 are polarized in the longitudinal direction while the longitudinal slots of linear arrays 33 are polarized in the transverse direction. The relative phase and amplitude of the electromagnetic energy feeding arrays and 33 are adjusted so that the fields radiated by linear arrays 10 are of equal amplitude and 90 out of phase with the fields radiated by arrays 33.

What is claimed is:

1. A linear array of radiating elements comprising a rectangular waveguide having first and second parallel narrow walls and first and second parallel broad walls for propagating electromagnetic energy of predetermined frequency therethrough; and a plurality of slots disposed transversely across said first narrow wall at uniform intervals of one-half guide wavelength at said predetermined frequency, alternate ones of said slots extending for respective predetermined distances less than midway across said first broad wall, and the remaining extremities of said alternate ones of said slots extending for distances greater than said respective predetermined distances but less than midway across said second broad wall, and the remaining slots of said plurality of slots extending for said respective predetermined distances into said second broad wall and the opposite extremities of said remaining slots extending for distances greater than said respective predetermined distances but less than midway across said first broad wall.

2. The linear array of radiating elements as defined in claim 1 additionally including means for providing first and second reflecting surfaces exterior to and normal to said first and seocnd broad walls, respectively, said first and second reflecting surfaces being disposed parallel to first narrow wall at a distance back therefrom greater than the extension of said slots into said first and second broad walls, said first and second reflecting surfaces having a width comparable to that of said first and second broad walls and lengths exceeding that of said plurality of slots by one guide wavelength at each extremity thereof.

3. A two-dimensional circularly polarized planar array comprising a first plurality of rectangular waveguides having first and second parallel narrow walls and first and second parallel broad walls for propagating electromagnetic energy of a predetermined frequency therethrough, said first narrow walls of said rectangular Waveguide being disposed in parallel in a common plane at a the extremities of said remaining slots extending for said predetermined distances into said second broad walls of said first plurality of rectangular waveguides and the opposite extremities of said remaining slots extending for distances greater than said predetermined distances into said first broad walls; a second plurality of rectangular waveguides having first and second narrow walls and first and second broad walls for propagating electromagnetic energy at said predetermined frequency therethrough, said second broad walls of said second plurality of rectangular waveguides being disposed in the plane of said second narrow walls of said first plurality of rectangular waveguides, and a plurality of longitudinal slots-disposed at intervals of one-half guide wavelength along said first broad walls of said second plurality of r'ectangular'waveguides, successivelongitudinal slots being disposed on alternate sides of the centerline of said first broad walls;

References Cited UNITED STATES PATENTS 2,932,823 4/1960 Beck et a1 343-771 PAUL L. GENSLER, Primary Examiner US. Cl. X.R. 343-834 

